Various types of earphones have been used in conjunction with audio reproduction apparatus in the past. The earphones are worn in the human ear to allow private sound reproduction.
Prior to explaining the structure and operation of earphones, the structure of the human ear will be briefly described with reference to FIGS. (1a) and 1(b). FIGS. 1(a) and 1(b) are front view and section of the leftside human ear. The rightside human ear is not shown, but has a similar structure symmetrical to the drawings. As shown in FIGS. 1(a) and 1(b), the human ear includes the auricle 10, the external ear 12 and the internal ear (not shown). The auricle 10 includes the tragus 14 and the antitragus 16 on both sides of the lower portion of the auricle 10. The tragus 14 and the antitragus 16 define the fossa 18 between them. The external ear 12 includes the concha cavity 20 and the external auditory meatus 22. An outer end of the concha cavity 20 is defined by the tragus 14 and the antitragus 16 and is connected to the fossa 18. An inner end of the concha cavity 20 is connected to the external auditory meatus 22. However, the external auditory meatus 22 is offset in the concha cavity 20 to the position near the tragus 14. The external auditory meatus 22 is terminated at the eardrum (not shown).
Referring now to FIGS. 2, 3 and 4, some typical examples of the conventional earphones will be described.
FIG. 2 shows a first example of the conventional earphone. As shown in FIG. 2(a), the earphone has a housing 30 for housing therein an audio transducer (not shown). The housing 30 may be shaped similarly to a marble. The marble-shaped housing 30 has a size to be retained in the concha cavity 20 of the human ear, as shown in FIG. 2(b).
The housing 30 is comprised of a front housing 32 for radiating sounds from the audio transducer and a rear housing 34. A hollow rod portion 36 is elongated from the rear housing 34. A signal cord 38 is connected to the audio transducer through the hollow rod portion 36. The hollow rod portion, i.e., the elongated portion 36, is positioned in the fossa 18 between the tragus 14 and the antitragus 16, when the earphone is worn in the ear. Then, the front housing 32 faces the external auditory meatus 22 of the ear.
The first conventional earphone of FIG. 2, however, has a drawback. That is, it is difficult to stably maintain the housing 30 in an accurate direction toward the external auditory meatus 22. This is because the external auditory meatus 22 is offset in the concha cavity 20, as described above. Further, the housing 30 easily fluctuates in the concha cavity 20. As a result, the sound level reproduced by the earphone and applied to the ear through the external auditory meatus 22 is reduced or the sound level easily fluctuates.
Furthermore, as the housing 30 does not fit in the concha cavity 20, a relatively large gap arises between the housing 30 and the concha cavity 20. The gap reduces the matching of the acoustic impedances between the earphone and the concha cavity 20 so that the frequency characteristic of the reproduced sound, particularly the characteristic in the low frequency range, is deteriorated.
FIG. 3 shows a second example of the conventional earphone. As shown in FIG. 3(a), the earphone has a housing 30 for housing therein an audio transducer (not shown). The housing 30 is shaped similar to a thick disc. The disc-shaped housing 30 has a size a little larger than the concha cavity 20 of the human ear. The housing 30 is worn in the ear by being engaged with the outside of the tragus 14 and the inside of the antitragus 16, as shown in FIG. 3(b).
The housing 30 is comprised of a front housing 32, for radiating sounds of the audio transducer, and a rear housing 34. A signal cord 38 is connected to the audio transducer through the rear housing 34. Further, the earphone has a tubular sound guide member 40. The tubular sound guide member 40 protrudes from the front housing 32 at the right axis of the housing 30. The tubular sound guide member 40 of the earphone is pushed into the external auditory meatus 22 of the ear so that the earphone is suspended on the ear by being engaged to the antitragus 16 and the external auditory meatus 22. In order to stably fit the earphone to the ear, the tubular sound guide member 40 has a relatively long length.
The second conventional earphone illustrated in FIG. 3 also has a drawback. That is, a user feels an unpleasant pressure sensation or a pain. This is because the earphone is worn in the ear with a relatively strong pressure. Particularly, the housing 30 is strongly pressed to the tragus 14 and the antitragus 16 for positioning the tubular sound guide member 40 in the external auditory meatus 22 which is offset in the concha cavity 20.
FIG. 4 shows a third example of the conventional earphone. As shown in FIG. 4(a), the earphone has a housing 30 for housing therein an audio transducer (not shown). The housing 30 is shaped similar to a thick disc. The disc-shaped housing 30 has a size to be retained in the concha cavity 20 of the human ear, as shown in FIG. 4(b).
The third conventional earphone has also a housing 30, an audio transducer (not shown) mounted in the housing 30, a signal cord 38 connected to the audio transducer without passing through an elongated portion, as shown in FIG. 4(a). The housing 30 is shaped similar to a thick disc, as the second one described above. However, the housing 30 has a smaller size than that of the second one so that the housing 30 entirely fits in the concha cavity 20 of the ear. Further, the earphone has a small tubular sound guide member 40. The small tubular sound guide member 40 is mounted to the front housing 30 at a position offset from the axis of the housing 30. Further the small tubular sound guide member 40 protrudes from the housing 30 in a slanted direction to the axis of the housing 30.
The housing 30 fits in the concha cavity 20 of the ear so that the small tubular sound guide member 40 is loosely fitted into the external auditory meatus 22, as shown in FIG. 4(b). On the other hand, the signal cord 11 is positioned above the tragus 14, as shown in FIG. 4(c).
The third conventional earphone of FIG. 4, also has a drawback. That is, it is difficult to stably wear the earphone in the ear. When an external force is applied to the earphone, the earphone can no longer be retained at a suitable position in the ear. Otherwise, the earphone falls from the ear. When the earphone is designed to fit stably in the ear, the housing 30 and the tubular sound guide member 40 must have a relatively large size. This, however, causes the same drawback as the earphone of FIG. 2. Thus, a user feels an unpleasant pressure sensation or a pain.
In addition, all the above-described conventional earphones are not proper in shape for using in a stereo earphone set. That is, a user finds it difficult in selecting the difference between the right and left earphones.